Method for Producing Highly Conformal Transparent Conducting Oxides

ABSTRACT

A method for forming a transparent conducting oxide product layer. The method includes use of precursors, such as tetrakis-(dimethylamino) tin and trimethyl indium, and selected use of dopants, such as SnO and ZnO for obtaining desired optical, electrical and structural properties for a highly conformal layer coating on a substrate. Ozone was also input as a reactive gas which enabled rapid production of the desired product layer.

STATEMENT OF GOVERNMENT INTEREST

The United States Government claims certain rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the United States Government and the University of Chicago and/or pursuant to DE-AC02-06CH11357 between the Untied States Government and UChicago Argonne, LLC representing Argonne National Laboratory.

FIELD OF THE INVENTION

This invention relates to a method and system for producing transparent conducting oxides. More particularly the invention relates to methods and systems for producing a variety of highly conformal transparent conducting oxides, such as, indium oxide, indium tin oxide, indium zinc oxide and tin zinc oxide.

BACKGROUND OF THE INVENTION

Transparent conducting oxides (“TCOs”) are important components for many applications, such as but not limited to: photovoltaic cells, flat panel displays, touch screens and architectural glass. Current methods of deposition, such as sputtering, are typically used; but production costs are in need of reduction; and quality of the product films need to be improved for various applications and also for providing layer uniformity over large areas. Previously, In₂O₃ deposition by ALD has been accomplished using InCl₃ with either H₂O or H₂O₂ as the oxygen source. Although useful for coating planar surfaces, this method suffers from several limitations. First, the InCl₃ chemistry requires high growth temperatures of 300° C. to 500° C., and yields a low growth rate of only 0.25-0.40 Å/cycle. In addition, the InCl₃ has a very low vapor pressure and must be heated to 285° C. just to saturate a planar surface. Furthermore, the corrosive HCl by-product can damage the deposition equipment. But the greatest limitation of the InCl₃/H₂O method, especially for coating nanoporous materials, is that InCl₃ can etch the deposited In₂O₃. Consequently, nanoporous materials require very long precursor exposures that are likely to completely remove the In₂O₃ from the outer portions of the nanoporous substrate.

An improved ALD process for In₂O₃ has also been sought for many years and a number of alternate precursors have been investigated including β-diketonates (In(hfac)₃ (hfac=hexafluoropentadionate), In(thd)₃ (thd=2,2,6,6-teramethyl-3,5-heptanedioneate), and In(acac)₃ (acac=2,4-pentanedionate)) and trimethyl indium (In(CH₃)₃). Unfortunately, these efforts were unsuccessful. No growth was observed using β-diketonates with water or hydrogen peroxide, while trimethyl indium did not yield self-limiting growth.

SUMMARY OF THE INVENTION

An improved method and system for producing indium oxide (In₂O₃) and other transparent conducting oxides is provided by the instant invention. In₂O₃ can also be doped with tin to form indium tin oxide (“ITO”) with improved electrical conductivity, high optical transparency and good chemical stability. Deposition of such materials is accomplished by using atomic layer deposition (“ALD”) to deposit ITO (and other such transparent conducting oxides) over large areas with high uniformity to address selected commercial applications. The ALD method is used in conjunction with particular precursor materials, such as trimethyl indium (TMIn”) due to its high vapor pressure, low cost and availability as a commodity. The ALD method is used with TMIn and O₃(ozone). In addition to ITO, other transparent conducting oxides can be prepared including, for example without limitation, doped ITO and tin zinc oxide. These and other features of the invention will be described in more detail hereinafter with reference to the figures described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a flow diagram of ALD;

FIG. 1B illustrates a gas pulsing cycle during ALD; and

FIG. 1C illustrates one cycle of an ALD process;

FIG. 2 illustrates an ALD reactor system;

FIG. 3 illustrates schematically the ALD process temperature window;

FIG. 4A shows deposition data of In₂O₃ by use of TMIn and H₂O;

FIG. 4B shows deposition data of In₂O₃ by use of TMIn and H₂O₂;

FIG. 4C shows deposition data of In₂O₃ by use of TMIn and O₂;

FIG. 4D shows deposition data of TMIn and O₃ (ozone); and

FIG. 4E shows deposition data of TMIn and O₃ for two ALD cycles(magnified image of FIG. 4D);

FIGS. 5A(1)-5A(5) shows process cycle conditions and

FIG. 5B show comparative growth for In₂O₃ by TMIn with H₂O and O₃;

FIG. 6 show comparative growth for In₂O₃ by TMIn with dosing O₃ or O₂;

FIG. 7A(1)-7A(4) illustrates deposition data of ALD In₂O₃ using TMIn and O₃ self limiting behavior growth;

FIG. 8A shows ALD In₂O₃ growth saturation data using TMIn and

FIG. 8B shows ALD growth saturation data using O₃;

FIG. 9A shows In₂O₃ thickness versus number of ALD cycles;

FIG. 9B shows index of refraction versus In₂O₃ thickness; and

FIG. 9C shows In₂O₃ thickness across a deposition surface;

FIG. 10A shows In₂O₃ growth rate versus deposition temperature and

FIG. 10B shows index of refraction of In₂O₃ versus deposition temperatures;

FIG. 11A shows an X-ray diffraction pattern for as deposited In₂O₃ at 150° C.;

FIG. 11B shows the layer of FIG. 11A annealed at 400 C for 6 h;

FIG. 12A shows transmission percent as a function of wavelength for In₂O₃ layers at various ALD cycles and annealed; and

FIG. 12B shows transmission percent for various as deposited cycles of ALD;

FIG. 13A shows In₂O₃ resistivity as a function of layer thickness;

FIG. 13B shows carrier concentration as a function of layer thickness; and

FIG. 13C shows Hall mobility as a function of layer thickness;

FIG. 14A shows an X-ray diffraction pattern for as deposited ALD layers of In₂O₃ deposited at selected temperatures; and

FIG. 14B shows these same layers after annealing at 400° C. for 6 h;

FIG. 15A shows resistivity for In₂O₃ before and after annealing;

FIG. 15B shows carrier concentration for In₂O₃ before and after annealing; and

FIG. 15C shows Hall mobility before and after annealing;

FIG. 16A shows percent transmittance for In₂O₃ layers deposited at various temperatures; and

FIG. 16B shows transmittance after being annealed;

FIG. 17A Tauc plot calculated from FIG. 16A for In₂O₃ layers as deposited at various temperatures and

FIG. 17B Tauc plot calculated for In₂O₃ layers as deposited at various number of ALD cycles;

FIG. 18 shows full range XPS scan of In₂O₃ after Ar sputter;

FIG. 19 shows deposition of SnO₂ using TDMASn and H₂O₂;

FIGS. 20A-20F show the ALD process for TDMASn with H₂O₂ and TMIn with O₃;

FIG. 21 shows a growth curve for alternate growth of TDMASn with H₂O₂ and TMIn with O₃;

FIG. 22 shows deposition of SnO₂ using TDMASn and O₃;

FIG. 23A shows a growth curve over time for TDMASn with In₂O₃ and SnO₂ cycles of three;

FIG. 23B shows alternate growth of In₂O₃ and SnO₂ for use of alternate growth cycles;

FIG. 24A shows X-ray diffraction patterns for ITO (10% Sn-90% In₂O₃) for different oxidizing environments and as deposited as well as annealed;

FIG. 24B shows percent transmittance for as deposited and annealed Sn₂O₃ deposited with Sn:O₃;

FIG. 24C shows percent transmittance for as deposited and annealed Sn₂O₃ deposited with Sn:H₂O₂;

FIG. 24D shows electrical resistivity for Sn:H₂O₂ and Sn:O₃;

FIG. 24E shows carrier concentration for SN:H₂O₂ and Sn:O₃;

FIG. 24F shows Hall mobility for Sn:H₂O₂ and Sn:O₃;

FIG. 25A shows X-ray diffraction patterns for as deposited ITO with various % Sn content;

FIG. 25B shows the ITO after annealing;

FIG. 25C shows percent transmittance for various % Sn deposited ITO;

FIG. 25D shows the layers of FIG. 25C after various annealing treatments;

FIG. 25E shows resistivity for various % SnO ALD cycles in In₂O₃;

FIG. 25F shows carrier concentration for the various % SnO ALD cycles;

FIG. 25G shows Hall mobility for the various of % SnO ALD cycles;

FIG. 26 shows layer thickness versus % doping in In₂O₃;

FIG. 27 shows XRF analysis of ITO for various amounts of Sn;

FIG. 28 shows after Ar sputter full scan XPS for as deposited 10% Sn ALD cycles in In₂O₃;

FIG. 29A show an X-ray diffraction pattern of ITO deposited on sapphire and

FIG. 29B shows ITO on fused silica;

FIGS. 30A-30F show process cycle conditions for deposition of ZnO-In₂O₃ layers using H₂O and O₃ with TMIn;

FIGS. 31A-31E show process cycle conditions for deposition of ZnO-In₂O₃ layers using O₃;

FIG. 32A shows the X-ray diffraction patterns for as deposited ZnO-In₂O₃ layers for various percentages of In₂O₃; FIG. 32B shows X-ray diffraction patterns for after annealed ZnO-In₂O₃ layers for various percentages of In₂O₃;

FIG. 33 shows optical transmittance for the as deposited layers of FIGS. 32A; and

FIG. 34A shows electrical resistivity for the various layers of FIG. 33;

FIG. 34B shows carrier concentration for the various layers of FIG. 33; and

FIG. 34C shows Hall mobility for the various layers of FIG. 33.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

In one form of the invention a system 10 is shown in FIG. 1A which illustrates a flow diagram of an atomic layer deposition (“ALD”) process used to form layers of transparent conducting oxides. In the system, 10 various gas sources are provided, such as for example, precursor sources 20 and inert gas 30 which are selectively output to reaction chamber 40. Vacuum pump 50 enables control of the vacuum level and/or pressure level of gases input to the reaction chamber 40. FIG. 1B illustrates an example of a cycle of gas level pulses during an ALD deposition cycle. FIG. 1C shows schematically one ALD cycle of gas pulsing and purges of the reaction chamber 40.

FIG. 2 illustrates further detail of a preferred form of an ALD system 60. The fundamentals of an ALD system are described in U.S. Pat. No. 4,058,430 which is incorporated by referenced herein. In the system 60 a reaction chamber 70 includes heaters 80, a flow tube 90 within which are disposed samples 100. Various precursor sources 110, 120 and 130 provide reactants and purge gases to the reaction chamber 70. The sources 110 can include, for example, trimethyl indium (“TMIn”), ozone (O₃), tin oxide (“SnO₂”) and zinc oxide (“ZnO”). The purge gases of the sources 120 and 130 include for example Ar, N₂ and other non-reactive gases. The system 60 further includes various valving systems 140 for processing deposition of selected transparent conducting oxides. In FIG. 3 is shown a schematic of an ALD process temperature window with areas of active ALD as well as condensation, incomplete reaction, decomposition and desorption regions of reaction. Consequently, proper ALD deposition is dependent on a particular temperature window for a growth precursor and desired oxide deposition. In various preferred embodiments described hereinafter, TMIn is applied to produce an In₂O₃ layer growth along with doping of In₂O₃ by Sn and Zn. Various temperatures were determined to provide productive ALD along with use of O₃. In addition, SnO-ZnO layer growth is described hereinafter.

In a preferred embodiment, In₂O₃ was deposited using the system 60 by use of the precursors TMIn and O₃, and was compared to unproductive uses of H₂O, H₂O₂ and O₂. This point is further amplified by reference to FIGS. 4A through 8B showing In₂O₃ growth rates under various conditions. The resulting In₂O₃ layers have highly desirable optical, electrical and mechanical/structural properties; and various properties are shown in FIGS. 9A through 18B, including for example, refractive index, optical transmittance, resistivity (with and without annealing step), carrier concentration, Hall mobility and X-ray diffraction patterns are illustrative of crystalline/amorphous structures (with and without annealing). FIG. 18 shows the various molecular orbital levels of the deposited In₂O₃ layers from an XPS scan.

In order to illustrate further the effectiveness of the use of O₃ to produce Sn₂O₃ deposition along with In₂O₃, FIGS. 19 through 29B illustrate growth curves for a variety of conditions, including co-deposition of In₂O₃, and data indicating achievement of Sn₂O₃ containing layers with desirable optical and electrical properties.

Other transparent conducting oxides can be deposited very effectively using O₃, such as Zn-In₂O₃, using the system 60 with precursors ZnO and TMIn to produce doped In₂O₃ layers. In FIGS. 30A through 32B are shown growth curves, again showing the effectiveness of the use of O₃ with precursors, to provide layers of In₂O₃ doped with ZnO. The resulting layers have excellent optical and electrical properties as shown by FIGS. 33 through 34C.

The preferred embodiments described hereinafter illustrate the advantageous features of forming transparent conducting oxides, such as In₂O₃ (doped and undoped) by use of TMIn and TDMAS_(n) tetrakis-(dimethylamino) tin and O₃ to produce layers with excellent optical, electrical and structural properties, contrary to conventional teachings. These layers enable application to a wide variety of commercial applications and produceable with greatly reduced cost and simplified system requirements.

The foregoing description of embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated. 

What is claimed is:
 1. A method of forming a transparent conducting oxide layer having a desired set of properties, comprising the steps of: providing an atomic layer deposition system; providing a substrate disposed in the atomic layer deposition system; inputting a precursor to the atomic layer deposition system; inputting ozone to the atomic layer deposition system; and forming a deposited layer on the substrate, wherein the deposited layer has the desired set of properties.
 2. The method as defined in claim 1 wherein the precursor and the ozone are input in a pulsed manner.
 3. The method as defined in claim 2 further including pulses of a gas in a purging step.
 4. The method as defined in claim 1 wherein the precursor comprises trimethyl indium.
 5. The method as defined in claim 1 further including a step of co-deposition of a dopant.
 6. The method as defined in claim 5 wherein the deposit is selected from the group of SnO and ZnO.
 7. The method as defined in claim 1 further including the step of controlling temperature in the atomic layer deposition system.
 8. The method as defined in claim 7 wherein the temperature ranges between about 100° C. to 150° C.
 9. The method as defined in claim 6 wherein the precursor is selected from the group of tetrakis-(dimethylamino) tin and trimethyl indium.
 10. The method as defined in claim 1 wherein the deposited layer has a structure selected from the group of amorphous, crystalline and mixtures thereof
 11. A transparent conducting oxide prepared by the steps of: providing an atomic layer deposition system; providing a substrate disposed in the atomic layer deposition system; inputting a precursor to the atomic layer deposition system; inputting ozone to the atomic layer deposition system; and forming a deposited layer on the substrate, wherein the deposited layer has the desired set of properties.
 12. The transparent conducting oxide as defined in claim 11 wherein the precursor includes trimethyl indium.
 13. The transparent conducting oxide as defined in claim 11 wherein the precursor and the ozone are input in a pulsed manner.
 14. The transparent conducting oxide as defined in claim 11 wherein the oxide comprises an In₂O₃ layer having a dopant therein.
 15. The transparent conducting oxide as defined in claim 11 wherein the precursor is selected from the group tetrakis-(dimethylamino) tin and trimethyl indium.
 16. The transparent conducting oxide as defined in claim 11 further including the step of inputting pulses of inert gas.
 17. The transparent conducting oxide as defined in claim 11 further including a step of co-deposition of a dopant.
 18. The transparent conducting oxide as defined in claim 17 wherein the dopant is selected from the group of SnO and ZnO.
 19. The transparent conducting oxide as defined in claim 11 further including the step of annealing the deposited layer.
 20. The transparent conducting oxide as defined in claim 11 further including the step of controlling temperature in the atomic layer deposition system. 